I have Firefox v 1.5.0.1 with the following extensions - PDF download, IE view, Public IP, FasterFox, Talkback and NoScript.
I'm having a minor problem with the Yahoo mail website. In the bulk email category I get a lot of junk emails.
Usually I click the "Check All" link - this would automatically check all the email boxes and then I'd click the "Delete" button.
But recently the 'Check All' link would work sometimes and sometimes doesn't. I'd need to refresh the page couple times before it would work. Same goes for other buttons as well ( Delete, Move etc.). I have no problems viewing Yahoo mail in IE.

...thanks for the tips. Changing the frequency from 3 to 1 removed the problem almost completely. I also removed Fasterfox which was setup in turbo mode - this was putting load on the web servers (according to the feature description). Doing this resolved the problems with the control buttons.